TY - JOUR
T1 - Importance of intracellular water apparent diffusion to the measurement of membrane permeability
AU - Sehy, Jonathan V.
AU - Banks, Alison A.
AU - Ackerman, Joseph J.H.
AU - Neil, Jeffrey J.
N1 - Funding Information:
The authors thank James Quirk for interesting discussions. This work was supported by National Institutes of Health grants NS35912 and R24-CA83060.
PY - 2002/11/1
Y1 - 2002/11/1
N2 - The exchange of water across biological membranes is of fundamental significance to both animal and plant physiology. Diffusional membrane permeability (Pd) for the Xenopus oocyte, an important model system for water channel investigation, is typically calculated from intracellular water pre-exchange lifetime, cell volume, and cell surface area. There is debate, however, whether intracellular water motion affects water lifetime, and thereby Pd. Mathematical modeling of water transport is problematic because the intracellular water diffusion rate constant (D) for cells is usually unknown. The measured permeability may be referred to as the apparent diffusional permeability, Pd, to acknowledge this potential error. Herein, we show that magnetic resonance (MR) spectroscopy can be used to measure oocyte water exchange with greater temporal resolution and higher signal-to-noise ratio than other methods. MR imaging can be used to assess both oocyte geometry and intracellular water diffusion for the same single cells. MR imaging is used to confirm the dependence of intracellular water lifetime on intracellular diffusion. A model is presented to relate intracellular lifetime to true membrane diffusional permeability. True water diffusional permeability (2.7 ± 0.4 μm/s) is shown to be 39 ± 6% greater than apparent diffusional permeability for 8 oocytes. This discrepancy increases with cell size and permeability (such as after water channel expression) and decreases with increasing intracellular water D.
AB - The exchange of water across biological membranes is of fundamental significance to both animal and plant physiology. Diffusional membrane permeability (Pd) for the Xenopus oocyte, an important model system for water channel investigation, is typically calculated from intracellular water pre-exchange lifetime, cell volume, and cell surface area. There is debate, however, whether intracellular water motion affects water lifetime, and thereby Pd. Mathematical modeling of water transport is problematic because the intracellular water diffusion rate constant (D) for cells is usually unknown. The measured permeability may be referred to as the apparent diffusional permeability, Pd, to acknowledge this potential error. Herein, we show that magnetic resonance (MR) spectroscopy can be used to measure oocyte water exchange with greater temporal resolution and higher signal-to-noise ratio than other methods. MR imaging can be used to assess both oocyte geometry and intracellular water diffusion for the same single cells. MR imaging is used to confirm the dependence of intracellular water lifetime on intracellular diffusion. A model is presented to relate intracellular lifetime to true membrane diffusional permeability. True water diffusional permeability (2.7 ± 0.4 μm/s) is shown to be 39 ± 6% greater than apparent diffusional permeability for 8 oocytes. This discrepancy increases with cell size and permeability (such as after water channel expression) and decreases with increasing intracellular water D.
UR - http://www.scopus.com/inward/record.url?scp=0036840514&partnerID=8YFLogxK
U2 - 10.1016/S0006-3495(02)75294-6
DO - 10.1016/S0006-3495(02)75294-6
M3 - Article
C2 - 12414717
AN - SCOPUS:0036840514
SN - 0006-3495
VL - 83
SP - 2856
EP - 2863
JO - Biophysical Journal
JF - Biophysical Journal
IS - 5
ER -